I’ve been meaning to write this post for a while. As UK government guidance has changed, face masks and face coverings will be very much the norm on public transport and in healthcare settings soon. So, now is a good time to consider whether face shields could play a role in preventing the spread of COVID-19.

Transatlantic colleagues Eli Perencevich, Daniel Diekema, and Michael Edmond have written a well thought-out opinion piece in JAMA making the case that face shields provide a viable – and in some ways superior – option to face masks for preventing the spread of COVID-19 outside of patient-care areas. The case for face shields has also been a prominent theme on the HAI Controversies blog (see here, for example).

As with any prevention measure, this goes back to our understanding of the way that SARS-CoV-2 is spread. Most of the evidence supports that SARS-CoV-2 is primarily spread in respiratory droplets, with contact and transmission through small aerosol particles secondary. (If SARS-CoV-2 was an “airborne” pathogen in the same way as, for example, measles, you’d expect R₀ and household attack rates to be much higher.)

There is – I think it’s fair to say – emerging evidence that face shields reduce the exposure to and emission of respiratory droplets considerably. If you can get comfortable that face shields provide adequate protection of the respiratory tract, they offer you the following benefits over a face mask:

• They cover your eyes in addition to your mouth and nose; they also cover your face so stop the prospect of a respiratory droplet landing on your face which is then (for want of a better word) smeared into contact with a mucous membrane.
• They make it much harder for you to touch your face (a bit like a dog collar for humans…!).
• They offer the potential for decontamination and reuse (although disposable is probably ideal).
• They have less chance of prompting the occupational hazards of long-term wearing face masks (painful / damaged ears and nose bridges).
• With a bit of thought, you could find a way to drink a cuppa and eat a sandwich with them on (possibly).
• It’s easier to communicate through them because people can see your whole face for expressions and lip reading.
• Supply chains are likely to be more robust for face shields than masks (and there are examples of where production lines have been repurposed for face shield production).

Most international guidelines recommend face coverings or medical/surgical masks to protect the respiratory tract from exposure to SARS-CoV-2 without direct reference to face shields. Although interesting to see the IDSA guidelines for easing COVID-19 distancing restrictions make a very brief reference to face shields in the same breath as masks). I hope that over time the evidence base for face shields will improve and they will be adopted widely because of the practical benefits over face coverings and masks.